The present invention relates to a Computed Tomography (CT) system for examining large objects such as rocket motors, ingots, pipes, etc., and is more particularly concerned with a novel handling arrangement, comprising a proximity bearing and associated elevator cup, adapted to rotate and elevate the object being examined.
CT systems per se are well known in the art, and comprise a source of radiation and an associated detector arranged to be rotated, or rotated and translated, relative to an object for purposes of examining a sectional slice of the object by means of penetrating radiation. The precision with which the positions of the X-ray source, detector and object are maintained and known is related directly to spatial resolution. The finer these precisions and accuracies are, the better the spatial quality of the final image will be. Accordingly, CT systems used heretofore are normally arranged to predetermine the positions of the X-ray source, detector and object relative to one another, and to maintain those relative positions during examination of the object slice. Such fixing and maintenance of position can be accomplished in a relatively straightforward manner when the object being examined is comparatively small in size, e.g., a portion of the human body.
When the object being examined does not lend itself to being positioned relative to the X-ray source and detector, other techniques must be employed to achieve a final image of acceptable spatial quality. If, for example, there are changes in the position of the axis of rotation of the object being examined and the expected position of that axis relative to the X-ray beam, such changes in position can be taken into account by use of either linear and/or angular monitoring equipment with feedback to the system, or by use of additional software and increased computer time needed to determine the center of rotation for each scan. These techniques increase the cost of the overall system and have limited applicability.
The problems discussed above become almost insurmountable when the object being examined is extremely large or unwieldy. In the case of a rocket motor, for example, which may typically have a length up to 25 feet, a diameter up to seven feet, a weight of 80,000 pounds and which contains a live propellant making it necessary to handle the rocket motor with extreme care, it has been virtually impossible heretofore to support and manipulate the motor with the precision needed for a CT examination thereof. While bearings are presently available which are sufficiently large to rotate a rocket motor of the dimensions specified, if the bearing or a rotary table with which it is associated is located adjacent one end of the rocket motor, e.g., as in the rocket motor inspection system described in Heffan et al U.S. Pat. No. 3,766,387, the normal bearing run-out, when magnified by an object which is as tall as a rocket motor, is unacceptable in a CT system.
The present invention is intended to obviate these problems by the provision of a novel handling system adapted to support and manipulate large objects in a fashion permitting examination thereof by known CT techniques.